Histone expression in metazoans is a highly regulated process that is linked with DNA synthesis during the cell cycle. Histone mRNA levels remain at a low basal level throughout most of the life of a cell but increase about 30-fold at the beginning of S phase, when DNA synthesis begins. At the end of S-phase, histone mRNA levels decrease back to basal level due to rapid degradation of the transcripts in the cytoplasm;however, little evidence exists to explain how degradation of histone mRNAs is triggered. The stem-loop binding protein (SLBP) is required for processing, export and translation of histone mRNAs. SLBP is also hypothesized to play a critical role in histone mRNA degradation by recognizing, or causing, aberrant translation termination and/or recruiting decay proteins to degrade the transcript. However, the role of SLBP In histone mRNA decay has not been thoroughly evaluated. I hypothesize that SLBP plays a critical role In recognizing, or causing, aberrant translation termination and/or in initiating mRNA degradation of histone mRNAs. Understanding how histone mRNA gene expression is coupled with DNA synthesis will give a clearer picture of how the concentration of histone proteins is controlled in a cell. Also, these studies will give insight into how a cell regulates gene expression during different stages of its life (e.g. after DNA synthesis). Therefore, completion of the proposed experiments will provide a better understanding of how disruption of this type of gene expression can result in abnormal cell growth and could lead to better treatments for cancer. Specific Aim 1: To identify the region(s) and specific amino acid residue(s) of SLBP that Is required for histone mRNA degradation. I will utilize various biochemical and molecular techniques to specifically search for domains and/or amino acid residues of SLBP that are required for this function. I will also search for amino acid residues that could signal histone mRNA decay by being post-translationally modified. Specific Aim 2: To determine if SLBP functions to recruit decay proteins to a histone transcript and/or to recognize aberrant translation termination. I will Identify proteins that interact with SLBP once DNA ^ synthesis is terminated. I will then disrupt these interactions and evaluate the effect those mutant During my graduate work, I analyzed els elements that are important for translation and in determining the stability of mRNAs in the yeast Saccharomyces cerevisiae. These studies have taught me basic molecular biological techniques that are essential for studying gene expression In eukaryotes. As a postdoctoral fellow in Dr. Marzluff's lab, I plan to study the regulation of decay of histone mRNAs in human cells. The results from these studies will help me understand how expression of histone mRNAs is regulated during the cell cycle, and provide^insights into the signals that are generated in the nucleus which ultimately lead to histone mRNA degradation in the cytoplasm. Additionally, these studies will expand my knowledge to include techniques in more complex eukaryotes and in biochemistry. My ultimate career goal is to obtain a faculty position where I can develop.an independent research program. I plan to study post-transcriptional gene regulation in eukaryotes and its role in human disease. I believe that the experience that I have obtained as a graduate student, together with the training and experience I will obtain as a postdoctoral fellow, will provide me with the necessary tools to initiate my own independent program aimed at successfully understanding how eukaryotes regulate gene expression post-transcriptionally.